1. Technical Field
The present invention relates to rotors for rotating electric machines that are used in, for example, motor vehicles as electric motors and electric generators.
2. Description of Related Art
There are known IPM (Interior Permanent Magnet) motors that have permanent magnets embedded in a rotor core. The IPM motors can use both reluctance torque and magnet torque, thereby achieving high efficiency. Therefore, the IPM motors are particularly suitable for use in hybrid and electric vehicles.
In addition, the IPM motors generally include a stator and a rotor disposed in radial opposition to the stator. The rotor includes a rotor core having a plurality of magnet-receiving holes arranged in a circumferential direction thereof and a plurality of permanent magnets each of which is received in one of the magnet-receiving holes of the rotor core. The permanent magnets form a plurality of magnetic poles, the polarities of which alternate between north and south in the circumferential direction of the rotor core.
Japanese Patent Application Publication No. JP2009124899A discloses an IPM synchronous motor that is designed to reduce the amount of permanent magnet material used and increase the total output torque.
Japanese Patent Application Publication No, JP2012161227A discloses a rotor for an IPM motor. In the rotor, each magnetic pole is formed of at least three permanent magnets. The rotor is designed to suppress magnetic saturation in each magnetic pole, thereby increasing the total output torque of the IPM motor.
However, in the known IPM motors, if the flux linkage is increased for the purpose of increasing the total output torque, torque ripple may occur due to magnetic saturation. In particular, in the rotors of the known IPM motors, it may be easy for magnetic saturation, which is the cause of torque reduction and torque ripple, to occur in q-axis core portions and those portions through which the permanent magnets are opposed to a stator. In addition, each of the q-axis core portions is located between one circumferentially-adjacent pair of the magnetic poles.